const message = "hello typescript"

// console.log(Boolean(message));  //true

console.log(!message);  // !把message转boolean 然后取反  =>false 
console.log(!!message); //true


let desc: string | null = null;
const content = desc ?? "??左侧没有值为null或undefined时-我就是默认值";
// const content = desc ? desc : "三目同上"
console.log(content);

export {}